In vivo evaluation of biomimetic fluorosurfactant polymer-coated expanded polytetrafluoroethylene vascular grafts in a porcine carotid artery bypass model

Abstract

Objective To evaluate the potential for biomimetic self-assembling fluorosurfactant polymer (FSP) coatings incorporating either heptamaltose (M7-FSP) to block non-specific protein adsorption, the cell adhesive RGD peptide (RGD-FSP), or the endothelial cell-selective CRRETAWAC peptide (cRRE-FSP) to improve patency and endothelialization in small diameter ePTFE vascular graft implants. Methods ePTFE vascular grafts (4 mm diameter, 5 cm length) were coated with either M7-FSP, RGD-FSP, or cRRE-FSP by dissolving FSPs in distilled water and flowing solution through the graft lumen for 24 h. Coatings were confirmed by receding water contact angle measurements on the lumen surface. RGD-FSP and cRRE-FSP grafts were pre-sodded in vitro with porcine pulmonary artery endothelial cells (PPAECs) using a custom-designed flow system. PPAEC coverage on the lumen surface was visualized with epifluorescent microscopy and quantified. Grafts were implanted as carotid artery interposition bypass grafts in 7 pigs for 33 ± 2 days (ePTFE n=3, M7-FSP n=4, RGD-FSP n=3, cRRE-FSP n=4). Patency was confirmed immediately after implant with duplex color-flow ultrasound and at explant with contrast-enhanced angiography. Grafts were sectioned for histology and stained: Movat’s pentachrome stain to outline vascular layers; immunofluorescent staining to identify endothelial cells (anti-von Willebrand factor antibody) and immunohistochemical staining to identify smooth muscle cells (anti-smooth muscle α-actin antibody). Neoinitima:lumen area ratio was determined to evaluate neointimal hyperplasia. Results Receding water contact angle measurements on graft luminal surfaces were significantly lower (P < .05) on FSP-coated ePTFE surfaces (M7-FSP: 40 ± 16°, RGD-FSP: 25 ± 10°, cRRE-FSP: 33 ± 16°) compared to uncoated ePTFE (126 ± 2°), confirming presence of the FSP layer. In vitro sodding of PPAECs on RGD-FSP and cRRE-FSP grafts resulted in a confluent monolayer of PPAECs on the luminal surface, with similar cell population on RGD-FSP (1200 ± 187 cells/mm2) and cRRE-FSP (1134 ± 153 cells/mm2) grafts. All grafts were patent immediately after implant, and 1/3 uncoated, 2/3 RGD-FSP, 2/4 M7-FSP, and 2/4 cRRE-FSP grafts remained patent after 1 month. PPAEC coverage of the lumen surface was seen in all patent grafts. RGD-FSP grafts had a slightly higher neointima:lumen area ratio (0.53 ± 0.06) compared to uncoated (0.29 ± 0.15), M7-FSP (0.20 ± 0.15), or cRRE-FSP (0.17 ± 0.09) grafts. Conclusion Biomimetic FSP coated ePTFE grafts can be utilized successfully in vivo and have potential to support endothelialization. Grafts modified with the M7-FSP and cRRE-FSP showed lower intimal hyperplasia compared to RGD-FSP grafts.

Dual biofunctional polymer modifications to address endothelialization and smooth muscle cell integration of ePTFE vascular grafts

“…While FSP presence on the adventitial surface is unnecessary from a biological standpoint, it is not expected to have an effect on cellular interactions at this surface since it is EC selective . Recently, FSP‐coated grafts fabricated in the same manner described herein and implanted in vivo as porcine carotid artery by‐passes showed no adverse tissue reaction at the adventitial surface, but rather demonstrated a normal inflammatory response similar to uncoated ePTFE grafts …”

“…18,31,32 Recently, FSP-coated grafts fabricated in the same manner described herein and implanted in vivo as porcine carotid artery by-passes showed no adverse tissue reaction at the adventitial surface, but rather demonstrated a normal inflammatory response similar to uncoated ePTFE grafts. 33 Since polymer coating of ePTFE grafts was performed sequentially, with the FSP coated first followed by hydrogel incorporation, there was concern that the hydrogel would cover the FSP coating on the lumen if the hydrogel penetrated beyond the thickness of the graft and into the luminal space. This outcome would be undesirable as it would mask the ECselective adhesion sites on the FSP necessary to develop an endothelial lining.…”

Bioactive coating of decellularized vascular grafts with a temperature-sensitive VEGF-conjugated hydrogel accelerates autologous endothelialization in vivo

“…Finally, after 8 weeks in vivo the non‐coated control group started to show a degree of endothelialization similar to that observed in the HG‐VEGF group, however, at this point intimal hyperplasia was significantly increased in the HG‐VEGF‐coated grafts compared with the non‐coated control group. Interestingly, increased neo‐intimal hyperplasia after bioactive luminal surface coating of vascular grafts has been observed in the same rodent aortic transplantation model (Assmann et al ., ; Aubin et al ., ), but also in different preclinical animal models (Bastijanic et al ., ) independent of the coating agent employed. Reasons for this still remain unclear, although in a clinical setting, such as polytetrafluoroethylene (PTFE) graft failure, neo‐intimal hyperplasia is commonly triggered by foreign body reaction, which, however, could neither be observed in this nor in the previous studies (Assmann et al ., ; Aubin et al ., ).…”

Customized Interface Biofunctionalization of Decellularized Extracellular Matrix: Toward Enhanced Endothelialization

“…This is consistent with previous in vivo findings, in which adventitial bioactive coating of dAoGs stimulated repopulation of the media region 21 and luminal fibronectin or RGD coating triggered neointima formation. 21,49 Nonetheless, further studies are warranted, evaluating the possible effects of customized biofunctionalization of dECM on in vivo endothelialization.…”

“…53 Nonetheless, current approaches, although enhancing in vivo endothelialization, have failed to prevent and even may lead to increased neointima formation. 21,49 This is particularly important as, for example, in the case of engineered vascular grafts, adverse neovessel remodeling directly leads to early and late graft failure. 13 Here, the integration of antiproliferative motifs preventing smooth muscle cell overproliferation 42 into a customized functionalization approach may pave the way to a new generation of multifunctional dECM scaffolds.…”